An airbag retainer ring is used for retaining an airbag cushion within an airbag module. An airbag module is employed in a vehicle, particularly an automobile, for protecting an occupant against injury by deploying an inflated airbag cushion to physically restrain the occupant's body when the automobile encounters a collision. A driver side airbag module normally includes an airbag cushion, an inflator for inflating the airbag cushion upon receiving a signal from a remote collision sensor, and a module baseplate mounting the airbag cushion and inflator. The inflator generally has a cylindrical sidewall extending through an inflator-receiving aperture of the module baseplate and an inflator flange extending radially outwardly from the sidewall and abutting a bottom surface of the baseplate. The airbag cushion has an open mouth formed by a collar that fits around the inflator with the collar positioned against a top surface of the baseplate. An airbag retainer ring is positioned on the collar of the airbag cushion and fits around the inflator sidewall, and fasteners such as bolts pass through the airbag retainer ring, the collar of the airbag cushion, the baseplate and the inflator flange and are fastened with nuts for example to secure the airbag module together.
During inflation of the airbag cushion, hot inflation gas radially exits the inflator through inflation ports in the inflator sidewall. It has been found that the hot inflation gas radially exiting the inflator can burn a "throat" of the airbag cushion extending from the collar and surrounding the inflator sidewall.
In order to avoid burning the airbag cushion, some airbag retainer rings include a perpendicular sidewall for deflecting the inflation gas to protect the collar and the throat of the airbag cushion. The perpendicular sidewall is spaced-apart from the inflator sidewall and extends up at least to a height equal with the inflation ports of the inflator. The perpendicular sidewall, therefore, intercepts the inflation gas and directs the inflation gas parallel with the inflator sidewall and generally axially into the airbag cushion.
While it is preferable that the inflation gas is directed away from the collar and the throat of the airbag cushion, it is also preferable that the inflation gases are directed radially into the airbag cushion. Radial inflation causes the airbag cushion to expand radially and evenly over the steering wheel, or "flatten out", and be fully inflated before an occupant is carried, by the force of deceleration caused by a collision of the vehicle, into the fully inflated and correctly positioned airbag cushion. In contrast, it has been found that axial inflation can cause the airbag cushion to be propelled axially and unevenly or "skewered", straight out of the airbag module towards the occupant until the airbag cushion reaches its maximum extension, and only then begin to fully inflate. Skewered inflation is unwanted because it can cause the top of airbag cushion to strike the occupant before being fully inflated. Skewered inflation can also cause the airbag cushion to push the occupant to the side of the inflating airbag cushion so that the occupant does not receive the protection of the inflated airbag cushion. Skewered inflation additionally places severe stress on the throat and the collar of the airbag cushion. While an airbag retainer ring having the perpendicular sidewall provides better protection against burning of the collar and throat of the airbag cushion, the perpendicular sidewall is believed to direct the inflation gas generally axially into the airbag cushion and, therefore, can encourage unwanted skewered inflation of the airbag cushion.
In order to reduce the chances of skewered inflation of the airbag cushion, some airbag retainer rings include an outwardly sloping sidewall, i.e. a sidewall that angle away from the inflator, as opposed to a perpendicular sidewall. The outwardly sloping sidewall intercepts and directs the inflation gas both axially and radially into the airbag cushion, and, therefore, reduces the chances of skewered inflation. The outwardly sloping sidewall, however, does not reduce cushion burning as well as the perpendicular sidewall. Accordingly, an airbag cushion used with a airbag retainer ring having an outwardly sloping sidewall may still need to incorporate a cushion tether to combat skewered inflation, and may also need protective layers of material positioned around the inside of its throat to combat airbag cushion burning.
It would be useful, therefore, to provide a cushion retainer that protects an airbag cushion from burning yet directs inflation gas into the airbag cushion such that the airbag cushion does not skewered upon inflation.